| With the development of laser spectroscopy and quantum optics,a series of nonlinear optical phenomena of atom-light interaction have been recognized.Based on these new physical phenomena,atomic magnetometers have been applied to detecting magnetic fields with high precision and high sensitivity.Compared with superconducting quantum interference devices(SQUID),atomic magnetometers also have approached a sensitivity of femtotesla level as ultra-sensitivity magnetic field detectors.Atomic magnetometers have already been used in weak magnetic field measurements and will play an important role in these fields.Atomic magnetometers detect magnetic fields based on coherent precession of polarized atomic spins,which are widely used in the fields of medicine,nuclear magnetic resonance,explosive detection and basic physics research.Nuclear magnetic resonance(NMR)spectroscopy has become a powerful tool for the detection of molecular structure and dynamics information,which has been widely used in physics,chemistry and biomedicine as well.Traditional NMR spectrometers use induction coil to carry out NMR experiments in high field.In order to obtain the high-sensitive and high-resolution NMR spectrum,NMR spectrometers usually develop towards a higher magnetic field direction.However,in order to achieve high magnetic fields,conventional spectrometers need large,immobile and expensive superconducting magnets,which limits the use of these technology.Atomic magnetometers can be used as a substitute for traditional induction coil,which make NMR technology extend to zero-field and low-field fields.We put forward a design scheme of atomic magnetometers and study the key technology of atomic magnetometers including the design methods of main components.The design,implementation and working principle of the zero-and low-field spectrometer are described in details.In this thesis,we also introduce the method to procuring low-field NMR signals,which mainly targets at non-coupling NMR samples.To sum up,the main research goals of this thesis are listed down below:(1)Atomic magnetometers have been demonstrated.The basic function of Nonlinear magneto-optical rotation(NMOR)magnetometer and Spin exchange relaxation free(SERF)magnetometer based on rubidium atom are realized.The research on NMOR magnetometer is mainly to solve the problem of material selections,so as to select suitable materials for the construction of the apparatus.The high-sensitivity SERF magnetometer as a detector of the zero-and low-field spectrometer is supposed to be working in the environment of high temperature and low field.For high temperature,we design a high performance of non-magnetic heating system,which can realize an accurately controlled heating(?0.1?)and long-term test under a high temperature up to 221?.For low field,a high performance magnetic shielding and compensation system is created,including magnetic shields and magnetic field compensation coils.The calculated magnetic noise of the magnetic shields MS-S is about 17.3 fT/Hz1/2 and that of MS-L is about 6.7 fT/Hz1/2,which is the key parameter for the design of atomic magnetometers.From the functional test of the atomic magnetometer,we obtain the characteristic signal with a linewidth of 4.9 nT and the magnetic field sensitivity about 33 fT/Hz1/2 at 32 Hz.The noise analysis is conducted to evaluate the performance of atomic magnetometers according to these test results.(2)The zero-and low-field spectrometer has been realized.The spectrometer is developed by using an atomic magnetometer and several kinds of sample transport shuttling devices.Specifically,we use the SERF magnetometer as a magnetic field sensor.In order to expand the application range of the magnetometer,we have designed and produced four kinds of sample shuttling devices,including the horizontal pneumatic shuttling,the flow type shuttling,the positioning pneumatic shuttling and the rotation type shuttling.In order to obtain the physical and chemical properties of samples,these sample shuttlings are used to transport samples to the detection region within the magnetic shields for detection.It can realize magnetic identification of material samples,low-field NMR study,static magnetic field measurements in situ,relaxation properties of NMR samples,and so on.(3)The low-field NMR has been studied using the zero-and low-field spectrometer.Without affecting the magnetic shielding performance,we have designed some special magnetic shielding openings.The spectrometer can be used in the low-field NMR research.Due to these unique openings combined with the precession magnetic field,the magnetometer enables to detect weak magnetic fields from samples by using the horizontal pneumatic shuttling to deliver samples to the detection region.These precession magnetic fields are provided by a solenoid coil.These magnetic resonance time-domain signals of the proton and fluorine nuclei have been experimentally measured in a single-shot sampling.These signals are close to oscillation attenuation signals.Under the about ?T precession magnetic field,the atomic magnetometer can also receive time-domain signals of NMR samples.Also,NMR signals of the proton-rich samples have been measured under different precessional magnetic fields.According to the positive correlation between precession magnetic fields and Larmor precession frequencies,these signals are confirmed to be NMR signals.These experiments have proved the advantage of using solenoid to provide precession magnetic fields.The application of solenoid benefits from the magnetic shielding design,which can also be proven the rationality of the design of MS-S and indirectly verify the effectiveness of the design of MS-L.We also have acquired NMR time-domain signals of proton and fluorine nuclei in the mixed solution of acetone and hexafluorobenzene.(4)Static magnetic field measurements can be used to detect long-term changes of the Earth's magnetic field,the magnetism of ancient rocks and the quantitative magnetic measurement of materials.Based on the low-field NMR,we demonstrate a method to measure static weak magnetic fields,where the static magnetic field's strength can be obtained by measuring nuclear spin precession's frequency.Atomic magnetometers can be adopted to sense the nuclear spin precession,and the nuclear spin can be adopted to measure the static magnetic field through this indirect method to obtain the static magnetic field's strength.According to uniform magnetic fields and small external leakage inside solenoid coils,we employ the solenoid provided by precession magnetic field.The positive precession magnetic field and reverse precession magnetic field are applied to the sample.According to the superposition principle of vector fields,internal residual magnetic fields and the magnetic field generated by the solenoid are superposed at the position of the sample to take the NMR information.We measure the axial residual magnetic field in the magnetic shields,where the magnetic field's strength is about 235 pT in the direction along the pump beam.By monitoring NMR signals from protons and fluorine nuclei,we realize a nuclear-spin comagnetometer,which can be used to detect static weak magnetic fields.The possibility of using a miniaturized atomic magnetometer sensor(MAMS)for static field measurements is also discussed.In this thesis,our magnetometer based on rubidium has a magnetic field sensitivity of about 33 fT/Hz1/2,which has been applied to measuring NMR signals of proton and fluorine nuclei.We demonstrate a method to measure static weak magnetic fields based on low-field NMR,where the static magnetic field's strength can be obtained by measuring nuclear spin precessional frequency.The zero-and low-field spectrometer has been realized,which provides a new platform for researches on NMR spectroscopy and extends the studies of NMR from traditional high field to low field as well as zero field.Additionally,the apparatus can provide a research platform within the fields of the nuclear magnetic resonance gyroscope(NMRG)and the unshielded atomic magnetometer. |
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